The background of the invention and its operation will be better understood with the following definitions in mind: Agonist--those muscles which normally contract for a given body movement; Antagonist--those muscles which normally elongate (stretch) for a given body movement; Isometric contraction-contraction of muscles where no body movement takes place.
Flexibility, the ability to move one's limbs and trunk freely through a wide range of motion, is important to the well being of all people. In simple terms a human motion is accomplished by contraction of one muscle group (henceforth called the agonist muscle group) to pull a body part in a given direction and the commensurate elongation or relaxation of an opposing muscle group (from now on referred to as the antagonist muscle group). Limited flexibility is usually the result of lack of strengthening the agonist muscle group and/or tense or shortened antagonist muscles. In normal healthy humans the limiting factor is usually the antagonist's inability to relax and stretch further.
The importance of flexibility has been particularly stressed by sports medicine experts as essential to athletic performance and the prevention of injuries. Various methods of stretching to increase flexibility have been investigated.. The method of ballistic stretching such as when one continually bobs up and down in an attempt to touch one's toes, has the disadvantage that the antagonist muscles (hamstrings and low back muscles ) have a difficult time elongating since they are called upon to contract (in order to reverse the direction of motion) at the limit of the stretch when they should be relaxing. Another disadvantage of the ballistic stretching technique is that the force involved with the motion has the potential of over stretching the antagonist muscles and injuring them.
A different method called static stretching has advantages over ballistic stretching. This technique involves a slow steady motion until the point of maximum stretch is obtained and this position is held for a period of time. The principle advantage is that the antagonist muscles are permitted to relax.
A still more effective method of increasing flexibility is achieved by employing the techniques of PNF. PNF is a large body of physical therapy techniques which utilize the actions of a therapist in conjunction with the patient to stimulate the patient's muscles to achieve a desired result. The PNF techniques were developed for paralytic patients at the Kabot-Kaiser Institute in Vallejo, Calif. A standard text on PNF techniques is "Proprioceptive Neuromuscular Facilitation, Patterns and Techniques" by M. Knott and D. E. Voss, published in 1956 by Hoeber and Harper of New York.
Modified PNF techniques for stretching have evolved from the traditional PNF techniques. These modified PNF stretching techniques have been shown in a number of studies to be superior to ballistic and static methods in achieving greater range of motion.
A specific example of PNF techniques applied to stretching is given using hip flexion as an example. The patient lies on his/her back with one leg resting on the ground. With the held of a therapist the patient raises the other leg (without bending the knee) toward his/her chest and continues in that direction until the antagonist muscle group (low back & hamstring) is stretched to the point that further motion would result in pain. At this point further motion (without pain) of the leg toward the chest can only be accomplished by the relaxation of the antagonist muscles.
One way to get muscles to relax is to stimulate them by hard contraction for a few seconds then release the tension. With the therapist's help the patient while at the limit of his stretch can contract the antagonist muscles (hamstring and low back) in an attempt to try to push his leg away from the chest in the opposite direction of the stretch. The therapist's role is to assure that the patient cannot move his leg away from his chest. This is referred to as isometric muscle contraction (meaning without motion). Some skill is required on the therapist's part to resist the motion without forcing the leg back towards the chest and possibly injuring the patient. After a few seconds of isometric contraction the natural relaxation response of the antagonists will allow the patient with the therapist's help to move the leg closer to the chest stretching further than he could previously.
At this new limit to stretch, the sequence can be repeated and perhaps repeated once more. Dramatic improvements in flexibility are readily obtained. These PNF stretching techniques are being taught by leading sports medicine figures to athletes wishing to improve their flexibility and along with it their athletic performance and resistance to injuries.
The PNF stretching technique described above involves the isometric contraction of the antagonist muscle group. According to the principles of PNF, however, there is also benefit to be gained from isometrically contracting the agonist muscle group (those muscles when contracted would move toward a greater degree of stretch) while at the limit of stretch. This effect can be understood in simple terms. As stated previously, any motion is accomplished by contraction of agonist muscles and relaxation of antagonist muscles. Therefore, the contraction of the agonist will naturally lead to the relaxation of the antagonist. However, for an unaided human at the limit of stretch, further contraction of the agonist will lead to painful elongation of the antagonist muscles. If the patient can contract the agonist muscles against a restraining force or structure, this isometric contraction will be accomplished without motion or the accompanying pain involved with further elongation of the antagonist muscles. This action facilitates the relaxation of the antagonist muscles.
The technique of isometrically contracting both the antagonist and the agonist sequentially at the limit of stretch, while extremely effective, is difficult to execute. While a therapist may successfully block the motion in either direction of a severely impaired individual, this is much more difficult to accomplish with a normal healthy patient. It is often difficult to completely block the attempted motion in one direction and much more difficult to be expected to restrain motion in the opposite direction. For this reason, most PNF stretching shown to athletes has been restricted to contraction of only the antagonist muscles at the limit of stretch, as described above.
A number of prior patents show various devices used to perform a variety of exercise routines. U.S. Pat. No. 3,285,070 shows a device for evaluating muscular strength and exercising. The device rigidly locks a body part at a given position. The user then attempts to move the body part and means are provided for measuring the effort applied. U.S. Pat. No. 3,233,366 shows a device for exercising involving either isotonic or isometric muscular contractions. U.S. Pat. No. 3,424,005 shows a device for isometric exercises with an indicator to signal the amount of force applied to a bar. U.S. Pat. No. 3,465,592 is an apparatus for isometric muscular exercises in which a body part movement is initiated by the user and may then be resisted by the device. U.S. Pat. No. 3,989,240 shows a power exerciser having power driven belts which extends and retracts to provide active physical exercise and passive body movement during physiotherapy. U.S. Pat. No. 4,478,411 shows a system for body exercises in which the body movement is resisted by weights that are raised and lowered. U.S. Pat. No. 4,669,450 shows an exercise device for operation by a foot of the user to apply a stretching force to a heel cord including mechanism for locking the foot board at a desired angular relationship to a leg board to maintain the application of a stretching force for desired period of time. U.S. Pat. No. 4,702,108 shows an apparatus and method for isometric muscle strength testing. U.S. Pat. No. 4,456,247 shows a leg stretching device for forcing the legs apart. None of such prior art patents are understood to show devices capable of performing the functions of applicant's invention.
Some equipment has been designed to exercise flexibility such as the devices described in the above mentioned U.S. Pat. Nos. 4,669,450 and 4,456,247. In all known cases these machines are not designed with PNF techniques in mind. They are designed to mechanically aid the user to achieve their limit of stretch and maintain that position. On some of the equipment the isometric contraction of the antagonist muscles could be performed, though in no cases does the literature of these machines suggest this action. In no case do these instruments allow the isometric contracting of the agonist muscles.
There also exist some machines which have been designed to test isometric strength which do provide rigid restraints against contracting of opposing muscle groups such as the devices described in the above mentioned U.S. Pat. Nos. 3,285,070 and 4,702,108. In these cases however, there is no provision for user controlled motion for stretching.